1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which can be used, for example, as a transmission for a vehicle.
2. Description of the Related Art
As an automatic transmission for a vehicle, there is conventionally used a toroidal-type continuously variable transmission.
In this type of toroidal-type continuously variable transmission, as shown in U.S. Pat. Nos. 5,099,710 or 5,286,240, there is used a structure in which a pair of input and output disks are combined together on the two sides of a set of power rollers so as to hold the power rollers. Specifically, the traction surfaces of the respective disks are formed in a convex-surface shape obtained by an arc, the center of which is the swing shaft of the power roller; and, in case where the power rollers are inclinedly rotated, the rotation radius ratio of the contact points between the power rollers and input and output disks is changed to thereby change gears.
In the toroidal-type continuously variable transmission, in order to secure the traction property, the power transmission between the input and output disks and power rollers is carried out in the following manner. That is, there are interposed oil films respectively between the traction surfaces of the input and output disks and the traction surfaces of the power rollers, and the power is transmitted by the shear forces of the oil films.
Therefore, in a variator which is composed of power rollers and input and output disks, there is employed a lubricating system which is peculiar to the toroidal-type continuously variable transmission and in which lubricating oil is finally sent out onto the traction surfaces of the toroidal-type continuously variable transmission input and output disks.
Conventionally, in this lubricating system, on the lower side of the variator, there is formed an oil collecting portion in which the lubricating oil can collect and, in the variator, there are formed a plurality of oil passages through which the lubricating oil can pass. And, the lubricating oil flowing out from the oil passages is allowed to flow to the traction surfaces of the input and output disks or to flow to the traction surfaces of the power rollers.
For example, as typically disclosed in JP-A-11-51141 and JP-A-11-210855, there is employed a structure in which, on the upper or lower side of the input and output disks, there formed injection holes respectively facing the traction surfaces of the respective disks and the lubricating oil is jetted out directly to the traction surfaces of the disks. In this type of toroidal-type continuously variable transmission, in order to maintain the stable lubricating performance, it is necessary to avoid the possibility that a foreign substance mixed into the lubricating oil can be bitten into the surface rolling contact points between the respective disks and power rollers.
In view of this, conventionally, in the toroidal-type continuously variable transmission, there is employed a structure in which a line filter is incorporated into the suction side of an oil pump to thereby remove foreign substances of a given size or larger.
However, sometimes, the line filter disposed on the suction side is unable to remove the foreign substances fully.
For example, in case where foreign substances such as dust slip into the oil passages respectively extending from the line filter to the injection holes in the assembling operation of the toroidal-type continuously variable transmission, or in case where burrs produced in the hole working operation remain in the openings of the oil passages, these foreign substances are jetted out onto the traction surfaces of the respective disks and the traction surfaces of the power rollers before they pass through the line filter.
Also, foreign substances made of metal remaining in the oil of an oil pan, sometimes, cannot be removed fully by the line filter but they are jetted out onto the traction surfaces.
In these cases, there is a fear that the foreign substances can be bitten into the rolling contact points between the disks and power rollers. And, even in case where the foreign substances are not bitten into the rolling contact points but are stored together with the lubricating oil on the lower side of the variator, there is a fear that the foreign substances in the oil (including foreign substances which have been previously present in the lubricating oil collecting in the oil collecting portion) can be caused to move violently due to the vibrations of the composing parts of the toroidal-type continuously variable transmission while it is in operation and can be bitten, together with the lubricating oil which is stored in the oil collecting portion and is scraped up by the disks, into the traction surfaces of the disks and power rollers again.
Such biting of the foreign substances reduces the lives of the input and output disks and power rollers.